The present invention relates generally to comminutors, sizing refiners and other machines for comminuting solid materials and, more particularly, to comminuting machines employing multiple rollers as the operative comminuting elements.
A wide variety of machines are known in industry for comminuting various types of solid material. Special purpose comminutors are known for comminuting diverse materials including coal, rock, wood, ore and refuse. For example, in the paper and pulp industries, comminutors commonly referred to as sizing refiners are employed to comminute wood waste to a size suitable for pulping. Other types of comminutors are used to produce wood chips for use in particle board. In the construction industry, heavy-duty comminutors of various types are used to produce crushed rock for use as gravel in concrete or in other construction applications. In the mining industry, ores are crushed to effect mineral separation in preparation for chemical or mechanical processing. Special purpose comminutors are employed in modern waste disposal facilities for comminuting garbage and solids in sewage prior to disposal or treatment.
One disadvantage of conventional comminutors is that they must be substantially overpowered to accommodate occasional overloading caused by relatively large or hard pieces of material fed into the machine. For example, in rock crushing machines having reciprocating jaw crushers, the machine must be sufficiently powerful to accommodate occasional overloading caused by a number of like-sized, relatively large rocks being fed at once into the jaws when the jaws are at a postion of maximum extension and thereby obtain a minimum of mechanical advantage in acting upon the rocks. Binding and jamming of the machine results if the machine is unable to crush the rocks under such circumstances. To avert this possibility, such machines are generally provided with a heavy-duty motor that can meet the occasional high power demands. The occasional peak power levels of such machines are much greater than their ordinary operating power levels, with the result that the external power supply to the comminutor must have an inordinately large peak power capacity. Where such comminutors are electrically powered, this requires high-power electrical hook-ups which are increasingly costly and difficult to obtain in many areas. The high peak power requirements of such comminutors also increase the size and expense of the structural components of the comminutors.
The above-mentioned problem is further aggravated by the fact that in most comminutors the material is constrained to pass through the machine at a relatively constant feed rate regardless of the force necessary to reduce it. This limits the capacity of the machine to process solid materials of varying hardness and size and also increases the likelihood of overloading and jam
Another common disadvantage of conventional comminutors is the high cost of repair and maintenance, particularly in the case of comminutors having comminuting elements which employ a cutting, shearing or chopping action. Such comminutors are typically used to comminute softer materials such as wood or refuse. Periodic maintenance and sharpening of the comminuting elements is necessary to keep the machine in satisfactory operating condition. Repairs are frequently necessitated by damage to the comminuting elements caused by inadvertent introduction of hard foreign objects into the machine. When such damage occurs, it is often extensive and is both difficult and costly to repair.
Further, many comminutors provide poor control over the consistency of the refined product. Specifically, a substantial portion of the comminuted material is often comminuted to an unnecessarily small size by overcomminuting or repeated comminuting of the same material. This results in a comminuted product having a large variation in particle size distribution, particularly in the smaller size ranges. Also, such unnecessary comminuting increases the energy consumption and overall cost of the process.
An example of a contemporary comminutor adapted particularly for comminuting wood waste is disclosed in the U.S. Pat. No. 4,120,458 to Hughes. The comminutor disclosed therein includes a plurality of toothed sprockets journalled substantially horizontally in the floor of an upright rotatable drum enclosure. In operation, solid material is introduced into the rotating drum enclosure and is driven in an orbital motion by engagement by a number of inwardly projecting vanes affixed to the inside of the drum. The weight of the rotating mass of material being upon the toothed sprockets causes the material to be reduced and comminuted until it is of a sufficiently small size to pass between the sprockets and out of the enclosure. Although this comminutor has proved to be adequate for its intended purposes, it is an object of the present invention to provide an improved comminutor whereby greater and more efficient forces may be brought to bear upon the solid material being comminuted. More specifically, it is an object of the present invention to provide a comminutor wherein the force with which solid material is driven against a set of comminuting elements is not limited to the force of gravity.
Accordingly, the general object and purpose of the present invention to provide an improved comminutor that is energy efficient and operates at a relatively constant power level.
It is also an object of the present invention to provide a comminutor that is of general applicability to solid materials of varying size, shape and hardness.
It is another object of the present invention to provide a comminutor that requires minimal maintenance and repair, and which is easily serviced and repaired when necessary.
It is yet another object and purpose of the present invention to provide a comminutor that screens the solid material, allowing only particles sufficiently reduced to be discharged, and yet which also avoids repeated comminuting or over-comminuting of material already sufficiently reduced.
It is also an object to provide a comminutor wherein exceptionally large or hard pieces of solid material are retained in the machine and continuously processed until sufficiently comminuted, without impairing or restricting the flow of other material through the comminutor.
It is yet another object of the present invention to provide a comminutor that allows close control over the size distribution of the comminuted product.